Re: Eat'n my own words

Posted by trucker40 on May 04, 2008 at 07:45:56 from (70.240.148.62):

In Reply to: Eat'n my own words posted by Lanse on May 03, 2008 at 18:46:17:

Did you plastiguage the crank?If you dont know how,plastiguage is a piece of plastic that looks like a hair wrapped in paper.The paper has stripes of different widths on it.You take a piece of it,put it on a clean crank,put new clean bearing shell in rod or main cap,torque down,take back apart,measure with gauge on the paper the ploastiguage comes in.That tells you your clearance between the bearing and the crank.When a motor is running the crank and rod bearings ride on a cushion of oil.There is no contact of the bearing and crank,until you start or stop the motor and oil pump quits pumping.The way it works is you have 1 to 3 thousandths of clearance between the bearing and the surface of the crank.More than that and you dont have oil pressure.No oil pressure and your bearings contact the crank,it causes friction because there is no oil cushion,and then you spin a bearing,causing you to rebuild motor,if you spin a main at least need line bored,rods can be resized,but its a lot of work and money when all you have to do is Plastiguage it first.Ask people at the parts store what clearance you need,and how to use it.You always need to do this when you build a motor or you run the risk of having a rod come through the side of the block.Dont go paint something,or do anything else until you plastiguage the bearings,if you havent done it yet.You also want to clean all the plastiguage off the crank and bearing shelll before you put it together.After I plastiguage mine,I take the crank back out,using a clean rag or paper towel with laquer thinner,solvent,or something,clean all the plastiguage off the crank.Oil the bearings in the block,put the crank back in,clean the bearing shell with solvent,blow dry with compressed air,put back in the caps,oil,put back together.It always has to be as clean as you can get it.Even if you have to wash your hands a few times to keep from getting dirt in there,you dont want any dirt or grit between the bearing shell and the cap,or between the bearing shell and the crank.After you get the crank in the block and torqued down finally,you grab the crank and spin it with one hand,if it doesnt spin freely in your well oiled bearing shells,something is wrong,and you have to find out what it is before you turn the crank any more,and before you put any rods in.There is only one way to build a motor,the right way.Sure you could get lucky and skip a bunch of steps and get it to run.It could run a while,or fly apart.You might have oil pressure,might not.Being as how you are a kid and anxious to hear it run,you might run it a while without oil pressure,and turn it into junk.Or it could run for 20 years.Try and take some guesswork out of it and check everything,then when you get done it could still blow up,but the chances of it blowing up after checking everything,and going over every bolt 2 times with a torque wrench is a lot less likely to happen.

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